1. Field of the Invention
This invention relates to actuation systems which are suitable for actuation of automatic sprinklers and other emergency devices. More particularly, this invention relates to an ultrafast acting thermally initiated actuation system, or, more simply, an ultrafast thermal actuator.
2. Description of the Prior Art
Automatic sprinklers employing a fusible element have enjoyed widespread commercial success for years. Devices of this type are shown, for example, in "Fire Protection Handbook," 15th edition, 1981, G. P. Kinnon, ed., Boston, National Fire Protection Association, pages 17-32 to 17-35, and in U.S. Pat. No. 3,314,482 to Young. Typically such an automatic sprinkler includes a discharge valve which is normally held shut by a mechanism which is directly connected to the fusible material. When a predetermined temperature is reached, the fusible material melts, releasing the link and lever mechanism and allowing the discharge valve to open. The fusible material may take various forms, e.g., a solder pellet or a link which includes a mass of fusible material. Sprinklers employing a link of this type are commonly referred link and lever type sprinklers. "Fire Protection Handbook" cited supra illustrates several link and lever type sprinklers. FIG. 17-3G (page 17-33) of "Fire Protection Handbook" illustrates a representative link and lever sprinkler comprising two levers which hold the sprinkler's discharge valve shut, and a link which includes a pair of metal members which are soldered together. The link is directly connected to the levers so that the levers hold the discharge valve closed under normal conditions. When the melting point of the solder is exceeded, the solder melts and the two link members separate, allowing the discharge valve to open.
Automatic sprinklers of the type described above have been useful primarily only for the control of fires rather than their suppression. According to Cheng Yao et al., Fire Journal, Jan. 1984, pages 42 to 46, the reason that such sprinklers are useful only for control rather than suppression of fires is their slow response time. This in turn is due to the large mass of the fusible link. As Yao et al. point out, faster response can be obtained by reducing the mass of the fusible link. Yao et al. on page 44 illustrate two fusible link type automatic sprinklers of similar structure except that the fast response sprinkler has a lower mass fusible link. The slower response sprinkler illustrated is similar to that shown in FIG. 17-3G (page 17-33) of "Fire Protection Handbook" cited supra. A convenient measure of thermal element sensitivity in sprinklers of this type is "response time index", or RTI, according to Yao et al. The more responsive the element is to temperature change, the lower its RTI value.
An automatic sprinkler of the type described above must be strong enough so that it will not rupture in its static or ready condition. Specifically, the fusible link must be strong enough to withstand the forces placed upon it and the lever mechanism by the high pressure water in the sprinkler. If the fusible link is made too thin, it cannot withstand these forces.
Also known are fire extinguisher actuation systems in which a thermally responsive member triggers a firing pin, which in turn initiates an explosive device which causes the fire extinguisher to open. U.S. Pat. No. 2,822,877 to Post, and U.S. Pat. No. 4,188,856 to Bendler et al., illustrate two such devices. No device of this type has achieved a degree of success even approaching that achieved by the fusible link type automatic sprinklers such as those shown in "Fire Protection Handbook" cited supra.
Reduction of the fusible link mass in conventional fusible link automatic sprinklers, as illustrated in Yao et al. cited supra, has probably gone as about as far as it can go. Further reduction of the fusible link mass would likely weaken the fusible link to the point that it could no longer be depended on to hold the link and the lever mechanism in place against the force of water under pressure under normal service conditions. Other types of automatic sprinklers have not found widespread acceptance. There exists a need for a new approach which will make possible a rugged and yet at the same time very fast-acting actuation system which can be used on automatic sprinklers.